The present invention relates to an absorbent sheet having at least two plies each including at least one embossed sheet of creped absorbent paper.
The invention relates in particular to an absorbent sheet intended for the field of wiping in a domestic or industrial application that is to say one that can be used as kitchen paper, towel, etc.
In the domestic or sanitary paper industry use is made, for producing the various products, of a creped absorbent paper with a low basis weight, usually ranging between 12 and 35 g/m2 per ply, such as cellulose fiber wadding or tissue paper. The ability of this material to stretch, which ability is conferred upon it by the creping operation, is put to good use for embossing it. The absorbent paper may be of the TAD (Through Air Dried) or alternatively of the CWP (Conventional Wet Pressed) type, these being two paper making techniques well known to those skilled in the art.
What happens is that embossing gives the sheet some bulk and improves its absorption of liquids, its feel and its softness. Attempts have also been made to increase the absorption capacity still further by creating multi-layer sheets which are obtained by combining at least two layers, also known as plies, each consisting of at least one of said embossed sheets.
There are two methods of embossing and assembling the plies in common use, and the one used depends on the desired properties of the end product.
The first is known in the art by the term “nested”. It consists first of all in embossing each of the plies separately so as to form, at the surface, protrusions which are generally substantially frustoconical or in the shape of pyramid frustums. Next, adhesive is applied to the tops of the protrusions of one of the plies and the plies are positioned in such a way that the faces exhibiting the protrusions face each other, the protrusions of one of them falling between the protrusions of the other. The plies are finally assembled in such a way that the protrusions that have been coated with adhesive fit or nest between the protrusions of the other ply. Thus, the two plies are connected by spots of glue between the tops of the protrusions of one ply and unembossed zones between the protrusions of the other ply. A structure is produced in which the voids formed are able to give the sheet improved absorption. Furthermore, the exterior faces are smooth and gentle to the touch because of the recessed zones formed by the backs of the protrusions. This technique is illustrated for example in U.S. Pat. No. 3,867,225.
Another known practice is to replace the adhesive bond by a mechanical connection achieved by knurling or marking.
A second method of assembly is known in the art as points/points. It differs from the previous mode of assembly in the relative positioning of the two plies. These, once they have been embossed separately, are brought together in such a way as to cause the tops of the protrusions to coincide with each other. The plies are joined together by the tops of the protrusions, points to points. This technique is illustrated in U.S. Pat. No. 3,414,459.
When considering the practical embodiments of these structures, whether they be of the “nested” or “points/points” type, it is found that the protrusions are often arranged in straight rows of uniform array or alternatively in patterns made up of polygonal figures, hexagons or diamonds, distributed uniformly in both directions, the machine direction and the cross direction, possibly in the form of arcs or curves, in particular forming sets which are uniformly distributed over the surface of a cut sheet.
Surprisingly, it has been found that certain properties of the product could be improved by choosing a different distribution of the protrusions on each absorbent sheet.